We shall employ laser Raman spectroscopy to measure accurately the pseudo-first-order rate constant (k) and Arrhenius parameters (Ea and A) governing isotopic hydrogen exchange at the 8C position of purine nucleotides in different structural and conformational states. The kinetic data will be obtained on mono-, oligo- and polynucleotide model compounds of known structure and conformation in order to correlate the slow hydrogen exchange reaction at 8C with the molecular environment of the purine ring. The kinetic data will be augmented with empirical MO calculations, as feasible, to help explain the role of electron withdrawing and donating groups, and ring protonations, on the lability of the 8C-H bond. The proposed research is expected to provide information on the roles of purine ring substituents, sugar-phosphate substituents, base stacking, base pairing and molecular conformation in determining the lability and accessibility to solvent of purinic 8C-H groups. We propose to use the correlations to investigate the molecular environment of purine residues in selected macromolecules and complexes. We shall investigate the 8C-H exchange properties of A and G residues of viral RNA and DNA in native viruses and after extraction from the viruses, as well as in partially assembled or disassembled virions. The exchange results will be interpreted to reveal features of nucleic acid structure and nucleoprotein interactions. The approach described above will also be applied to different states of nucleotide coenzymes to reveal whether the molecular environment of the purine ring is altered by oxidation-reduction processes and enzyme binding.